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428 lines
12 KiB
C
428 lines
12 KiB
C
/*
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* Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the OpenSSL license (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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* in the file LICENSE in the source distribution or at
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* https://www.openssl.org/source/license.html
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*/
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#include <stdio.h>
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#include "internal/cryptlib.h"
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#include "internal/bn_int.h"
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#include <openssl/bn.h>
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#include <openssl/sha.h>
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#include "dsa_locl.h"
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#include <openssl/asn1.h>
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static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
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static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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BIGNUM **rp);
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static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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BIGNUM **rp, const unsigned char *dgst, int dlen);
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static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
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DSA_SIG *sig, DSA *dsa);
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static int dsa_init(DSA *dsa);
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static int dsa_finish(DSA *dsa);
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static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
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BN_CTX *ctx);
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static DSA_METHOD openssl_dsa_meth = {
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"OpenSSL DSA method",
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dsa_do_sign,
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dsa_sign_setup_no_digest,
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dsa_do_verify,
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NULL, /* dsa_mod_exp, */
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NULL, /* dsa_bn_mod_exp, */
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dsa_init,
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dsa_finish,
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DSA_FLAG_FIPS_METHOD,
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NULL,
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NULL,
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NULL
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};
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static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
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void DSA_set_default_method(const DSA_METHOD *meth)
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{
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default_DSA_method = meth;
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}
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const DSA_METHOD *DSA_get_default_method(void)
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{
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return default_DSA_method;
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}
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const DSA_METHOD *DSA_OpenSSL(void)
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{
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return &openssl_dsa_meth;
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}
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static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
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{
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BIGNUM *kinv = NULL;
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BIGNUM *m, *blind, *blindm, *tmp;
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BN_CTX *ctx = NULL;
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int reason = ERR_R_BN_LIB;
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DSA_SIG *ret = NULL;
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int rv = 0;
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if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) {
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reason = DSA_R_MISSING_PARAMETERS;
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goto err;
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}
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ret = DSA_SIG_new();
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if (ret == NULL)
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goto err;
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ret->r = BN_new();
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ret->s = BN_new();
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if (ret->r == NULL || ret->s == NULL)
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goto err;
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ctx = BN_CTX_new();
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if (ctx == NULL)
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goto err;
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m = BN_CTX_get(ctx);
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blind = BN_CTX_get(ctx);
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blindm = BN_CTX_get(ctx);
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tmp = BN_CTX_get(ctx);
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if (tmp == NULL)
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goto err;
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redo:
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if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
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goto err;
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if (dlen > BN_num_bytes(dsa->q))
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/*
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* if the digest length is greater than the size of q use the
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* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
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* 4.2
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*/
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dlen = BN_num_bytes(dsa->q);
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if (BN_bin2bn(dgst, dlen, m) == NULL)
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goto err;
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/*
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* The normal signature calculation is:
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*
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* s := k^-1 * (m + r * priv_key) mod q
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*
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* We will blind this to protect against side channel attacks
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*
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* s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
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*/
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/* Generate a blinding value */
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do {
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if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1,
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BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
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goto err;
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} while (BN_is_zero(blind));
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BN_set_flags(blind, BN_FLG_CONSTTIME);
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BN_set_flags(blindm, BN_FLG_CONSTTIME);
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BN_set_flags(tmp, BN_FLG_CONSTTIME);
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/* tmp := blind * priv_key * r mod q */
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if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx))
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goto err;
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if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx))
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goto err;
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/* blindm := blind * m mod q */
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if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx))
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goto err;
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/* s : = (blind * priv_key * r) + (blind * m) mod q */
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if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q))
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goto err;
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/* s := s * k^-1 mod q */
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if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
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goto err;
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/* s:= s * blind^-1 mod q */
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if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL)
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goto err;
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if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx))
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goto err;
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/*
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* Redo if r or s is zero as required by FIPS 186-3: this is very
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* unlikely.
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*/
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if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
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goto redo;
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rv = 1;
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err:
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if (rv == 0) {
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DSAerr(DSA_F_DSA_DO_SIGN, reason);
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DSA_SIG_free(ret);
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ret = NULL;
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}
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BN_CTX_free(ctx);
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BN_clear_free(kinv);
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return ret;
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}
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static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
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BIGNUM **kinvp, BIGNUM **rp)
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{
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return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
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}
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static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
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BIGNUM **kinvp, BIGNUM **rp,
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const unsigned char *dgst, int dlen)
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{
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BN_CTX *ctx = NULL;
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BIGNUM *k, *kinv = NULL, *r = *rp;
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BIGNUM *l;
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int ret = 0;
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int q_bits, q_words;
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if (!dsa->p || !dsa->q || !dsa->g) {
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DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
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return 0;
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}
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k = BN_new();
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l = BN_new();
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if (k == NULL || l == NULL)
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goto err;
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if (ctx_in == NULL) {
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if ((ctx = BN_CTX_new()) == NULL)
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goto err;
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} else
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ctx = ctx_in;
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/* Preallocate space */
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q_bits = BN_num_bits(dsa->q);
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q_words = bn_get_top(dsa->q);
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if (!bn_wexpand(k, q_words + 2)
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|| !bn_wexpand(l, q_words + 2))
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goto err;
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/* Get random k */
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do {
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if (dgst != NULL) {
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/*
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* We calculate k from SHA512(private_key + H(message) + random).
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* This protects the private key from a weak PRNG.
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*/
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if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
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dlen, ctx))
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goto err;
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} else if (!BN_priv_rand_range(k, dsa->q))
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goto err;
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} while (BN_is_zero(k));
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BN_set_flags(k, BN_FLG_CONSTTIME);
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BN_set_flags(l, BN_FLG_CONSTTIME);
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if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
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if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
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dsa->lock, dsa->p, ctx))
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goto err;
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}
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/* Compute r = (g^k mod p) mod q */
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/*
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* We do not want timing information to leak the length of k, so we
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* compute G^k using an equivalent scalar of fixed bit-length.
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*
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* We unconditionally perform both of these additions to prevent a
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* small timing information leakage. We then choose the sum that is
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* one bit longer than the modulus.
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*
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* There are some concerns about the efficacy of doing this. More
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* specificly refer to the discussion starting with:
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* https://github.com/openssl/openssl/pull/7486#discussion_r228323705
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* The fix is to rework BN so these gymnastics aren't required.
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*/
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if (!BN_add(l, k, dsa->q)
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|| !BN_add(k, l, dsa->q))
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goto err;
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BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);
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if ((dsa)->meth->bn_mod_exp != NULL) {
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if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
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dsa->method_mont_p))
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goto err;
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} else {
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if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
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goto err;
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}
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if (!BN_mod(r, r, dsa->q, ctx))
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goto err;
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/* Compute part of 's = inv(k) (m + xr) mod q' */
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if ((kinv = dsa_mod_inverse_fermat(k, dsa->q, ctx)) == NULL)
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goto err;
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BN_clear_free(*kinvp);
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*kinvp = kinv;
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kinv = NULL;
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ret = 1;
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err:
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if (!ret)
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DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
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if (ctx != ctx_in)
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BN_CTX_free(ctx);
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BN_clear_free(k);
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BN_clear_free(l);
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return ret;
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}
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static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
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DSA_SIG *sig, DSA *dsa)
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{
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BN_CTX *ctx;
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BIGNUM *u1, *u2, *t1;
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BN_MONT_CTX *mont = NULL;
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const BIGNUM *r, *s;
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int ret = -1, i;
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if (!dsa->p || !dsa->q || !dsa->g) {
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DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
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return -1;
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}
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i = BN_num_bits(dsa->q);
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/* fips 186-3 allows only different sizes for q */
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if (i != 160 && i != 224 && i != 256) {
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DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
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return -1;
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}
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if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
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DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
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return -1;
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}
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u1 = BN_new();
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u2 = BN_new();
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t1 = BN_new();
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ctx = BN_CTX_new();
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if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
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goto err;
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DSA_SIG_get0(sig, &r, &s);
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if (BN_is_zero(r) || BN_is_negative(r) ||
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BN_ucmp(r, dsa->q) >= 0) {
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ret = 0;
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goto err;
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}
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if (BN_is_zero(s) || BN_is_negative(s) ||
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BN_ucmp(s, dsa->q) >= 0) {
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ret = 0;
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goto err;
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}
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/*
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* Calculate W = inv(S) mod Q save W in u2
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*/
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if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
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goto err;
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/* save M in u1 */
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if (dgst_len > (i >> 3))
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/*
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* if the digest length is greater than the size of q use the
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* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
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* 4.2
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*/
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dgst_len = (i >> 3);
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if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
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goto err;
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/* u1 = M * w mod q */
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if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
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goto err;
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/* u2 = r * w mod q */
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if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
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goto err;
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if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
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mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
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dsa->lock, dsa->p, ctx);
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if (!mont)
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goto err;
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}
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if (dsa->meth->dsa_mod_exp != NULL) {
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if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
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dsa->p, ctx, mont))
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goto err;
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} else {
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if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
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mont))
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goto err;
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}
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/* let u1 = u1 mod q */
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if (!BN_mod(u1, t1, dsa->q, ctx))
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goto err;
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/*
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* V is now in u1. If the signature is correct, it will be equal to R.
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*/
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ret = (BN_ucmp(u1, r) == 0);
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err:
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if (ret < 0)
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DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
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BN_CTX_free(ctx);
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BN_free(u1);
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BN_free(u2);
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BN_free(t1);
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return ret;
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}
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static int dsa_init(DSA *dsa)
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{
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dsa->flags |= DSA_FLAG_CACHE_MONT_P;
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return 1;
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}
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static int dsa_finish(DSA *dsa)
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{
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BN_MONT_CTX_free(dsa->method_mont_p);
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return 1;
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}
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/*
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* Compute the inverse of k modulo q.
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* Since q is prime, Fermat's Little Theorem applies, which reduces this to
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* mod-exp operation. Both the exponent and modulus are public information
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* so a mod-exp that doesn't leak the base is sufficient. A newly allocated
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* BIGNUM is returned which the caller must free.
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*/
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static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
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BN_CTX *ctx)
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{
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BIGNUM *res = NULL;
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BIGNUM *r, *e;
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if ((r = BN_new()) == NULL)
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return NULL;
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BN_CTX_start(ctx);
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if ((e = BN_CTX_get(ctx)) != NULL
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&& BN_set_word(r, 2)
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&& BN_sub(e, q, r)
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&& BN_mod_exp_mont(r, k, e, q, ctx, NULL))
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res = r;
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else
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BN_free(r);
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BN_CTX_end(ctx);
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return res;
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}
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